name resolution for guard patterns #140746
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I'll be modifying it in future commits, so I think it's cleanest to abstract it out. Possibly a newtype would be ideal, but for now this is least disruptive.
This splits introduction of bindings into scope (`apply_pattern_bindings`) apart from manipulation of the pattern's binding map (`fresh_binding`). By delaying the latter, we can keep bindings from appearing in-scope in guards. Since `fresh_binding` is now specifically for manipulating a pattern's bindings map, this commit also inlines a use of `fresh_binding` that was only adding to the innermost rib.
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This PR provides an initial implementation of name resolution for guard patterns (RFC 3637). This does not change the requirement that the bindings on either side of an or-pattern must be the same (proposal here); the code that handles that is separate from what this PR touches, so I'm saving it for a follow-up.
On a technical level, this separates "collecting the bindings in a pattern" (which was already done for or-patterns) from "introducing those bindings into scope". I believe the approach used here can be extended straightforwardly in the future to work with
if letguard patterns, but I haven't tried it myself since we don't allow those yet.Tracking issue for guard patterns: #129967
cc @Nadrieril